Low draw volume analyte detection systems

Abstract

Systems and methods for determining the concentration of an analyte in a sample such as bodily fluid are disclosed. Systems and methods disclosed herein comprise reducing the volume of sample withdrawn from the source of biological fluid. Low draw volume systems can be implemented using small inner diameter tube, valves and one or more sensors, for example. A method for calibrating a measurement of an analyte in a fluid sample for dilution of the fluid sample is also disclosed.

1 . A low draw volume analyte detection system for determining the concentration of one or more analytes in a sample of biological fluid, the system comprising:
 a main analysis and control instrument; and   a fluid handling module removably engageable with said main analysis and control instrument;   said main analysis and control instrument comprising:
 a body fluid analyzer configured to analyze at least one component of a sample of bodily fluid and determine the concentration of at least one analyte in said component of the sample of body fluid; and 
 a fluid system in fluidic communication with a patient and configured to withdraw a sample of bodily fluid from the patient, said fluid system comprising:
 a first fluid passageway fluidically connected to the patient and a fluid junction, said first fluid passageway having an inner diameter; 
 a second fluid passageway comprising a body fluid sensor configured to sense the presence of and/or a property of the body fluid, wherein said second fluid passageway is fluidically connected to the fluid junction, said second fluid passageway having an inner diameter different from the inner diameter of the first fluid passageway; 
 a third fluid passageway in fluid communication with the fluid junction and the fluid handling module, said third fluid passageway having an inner diameter different from the inner diameter of the first fluid passageway; and 
 at least one flow regulating device configured to control the fluid flow across the fluid junction. 
 
   
     
     
         2 . The low draw volume system of  claim 1 , wherein the inner diameter of the second fluid passageway is greater than the inner diameter of the first fluid passageway. 
     
     
         3 . The low draw volume system of  claim 1 , wherein the inner diameter of the third fluid passageway is smaller than the inner diameter of the first fluid passageway 
     
     
         4 . The low draw volume system of  claim 1 , wherein the inner diameter of the first fluid passageway has a value between approximately 0.025 inches and approximately 0.035 inches. 
     
     
         5 . The low draw volume system of  claim 1 , wherein the inner diameter of the second fluid passageway has a value between approximately 0.036 inches and approximately 0.045 inches. 
     
     
         6 . The low draw volume system of  claim 1 , wherein the inner diameter of the third fluid passageway has a value between approximately 0.015 inches and approximately 0.024 inches. 
     
     
         7 . The low draw volume system of  claim 1 , wherein the volume of sample withdrawn from the patient lies between approximately 2 ml per minute to approximately 3 ml per minute. 
     
     
         8 . The low draw volume system of  claim 1 , wherein the volume of sample withdrawn from the patient lies between approximately 150 ml per day to approximately 500 ml per day. 
     
     
         9 . A method of monitoring the concentration of one or more analytes in a sample of biological fluid while reducing fluid loss from a fluid source, said method comprising:
 periodically withdrawing a low volume of a fluid from a source of biological fluid;   sensing a property of the withdrawn fluid using one or more sensors;   dividing the withdrawn volume of fluid into at least a return portion and an analysis portion;   analyzing the analysis portion to determine one or more properties of the constituents of the fluid;   recording said one or more properties of the constituents of the fluid to track the concentration of one or more analytes; and   returning a return portion to the source;   wherein the analysis portion is smaller than the return portion, thereby reducing fluid loss from the source of biological fluid per analysis cycle and allowing an increase in the frequency of analysis so as to provide increased analyte concentration data to a care provider.   
     
     
         10 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing between approximately 2.0 ml-6.0 ml of the fluid in a draw period of less than minutes. 
     
     
         11 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing less than approximately 150 ml of fluid per day. 
     
     
         12 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing between approximately 100 ml-200 ml of fluid per day. 
     
     
         13 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing between approximately 200 ml-300 ml of fluid per day such that the interval between fluid withdrawals is approximately 15 minutes. 
     
     
         14 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing between approximately 300 ml-400 ml of fluid per day such that the number of times fluid is withdrawn per day is at least 48. 
     
     
         15 . The method of  claim 9 , wherein withdrawing a low volume of fluid comprises withdrawing between approximately 400 ml-500 ml of fluid per day. 
     
     
         16 . The method of  claim 9 , wherein the method further comprises providing a small inner diameter tube to achieve withdrawing a low volume of fluid. 
     
     
         17 . The method of  claim 16 , wherein providing a small inner diameter tube comprises providing a tube with inner diameter less than approximately 0.04 inches. 
     
     
         18 . The method of  claim 9 , wherein dividing the withdrawn fluid comprises dividing the withdrawn fluid into an analyte portion and a return portion such that the analyte portion has a volume between 1 μl and 100 μl. 
     
     
         19 . A method of reducing a volume of fluid drawn from a source of biological fluid for determining the concentration of one or more analytes in the fluid, the reduction method comprising:
 providing a fluid system configured to tap in to a source of biological fluid, said fluid system comprising multiple fluid passageways that are in fluid communication with a fluid junction, wherein a first fluid passageway of the multiple fluid passageways has an inner diameter that is different from the inner diameter of a second fluid passageway of the multiple fluid passageways;   drawing a volume of fluid from the source of biological fluid into the first fluid passageway by establishing a pressure gradient;   continuing to draw a continuous column of fluid from the source of biological fluid into and through the first fluid passageway until a leading edge of the continuous column reaches a sensor;   sensing a leading edge of the withdrawn fluid using the sensor;   in response to sensing the leading edge, closing a first valve in the first fluid passageway between the leading edge and the source of biological fluid to separate a sample portion—located between the first valve and the leading edge—from a return portion—located between the first valve and the source of biological fluid—and directing the sample to flow from the first fluid passageway into a second fluid passageway past the first valve;   analyzing said sample to determine the concentration of one or more analytes; and   returning the return portion to the source of biological fluid using the first valve and by establishing a pressure gradient;   wherein the first valve is positioned closer to the sensor than to the fluid source and the sample volume is less than the volume of the return portion, thereby reducing the volume of fluid that is never returned to the source of fluid and allowing an increased number of withdrawal and measurement events without harm to a fluid source.   
     
     
         20 . The method of  claim 19 , wherein the method comprises providing a fluid passageway with inner diameter less than 0.04 inches to withdraw a low volume of fluid from the source. 
     
     
         21 . The method of  claim 19 , wherein the method comprises withdrawing between 2 ml and 3 ml of fluid in a certain interval. 
     
     
         22 . The method of  claim 19 , wherein the method comprises sensing the leading edge of the withdrawn fluid using a hemoglobin sensor. 
     
     
         23 . The method of  claim 19 , wherein the method comprises sensing the leading edge of the withdrawn fluid using a bubble sensor. 
     
     
         24 . The method of  claim 19 , wherein the method comprises establishing the pressure gradient using a vacuum pump. 
     
     
         25 . The method of  claim 19 , wherein dividing the withdrawn fluid comprises dividing the withdrawn fluid into a first and second portion such that the volume of the first portion is between 1 μl and 10 μl. 
     
     
         26 . A method of limiting the withdrawn volume of a biological sample that is used for analysis and not returned to the source, the method comprising:
 automatically withdrawing a volume of biological sample into an analyte monitoring apparatus through a tube having an inner diameter of between approximately 0.025 inches and 0.04 inches;   sensing the arrival of a leading edge of the biological sample at a first sensor;   separating the biological sample into an analysis portion not exceeding 500 μl and a return portion;   returning the return portion back through the tube to the source;   further separating the analysis portion into slugs by injecting separation volumes of separation fluid into the analysis portion, the separation fluid being generally immiscible with the biological fluid;   urging the slugs of the analysis portion and the separation volumes of separation fluid through a fluid pathway toward an analyte sensor;   using the distinct edges of the slugs created by the separation volumes of separation fluid to identify arrival of at least one slug of the analysis portion at the analyte sensor, thereby limiting the withdrawn volume of the biological sample that is used for analysis; and   automatically preventing the slugs of the analysis portion and separation volumes of separation fluid from returning to the source.